1. Field of the Invention
The present invention relates to a light emitting device.
2. Description of the Related Art
A light emitting diode (LED), a type of light emitting device which constitutes a light emission source by using a compound material such as GaAs, AlGaAs, GaN, InGaN, AlGaInP, or the like, is a semiconductor device capable of generating light of various colors according to the recombination of electrons and holes at p and n type semiconductor junctions when current is applied thereto.
An LED is environmentally-friendly, has a fast response time in the range of a few nano-seconds to thus be effective for a video signal stream, and is available for impulsive driving.
In addition, an LED has a color gamut of 100% or higher, can arbitrarily change the luminance of light, color temperature, or the like, by adjusting the quantity of light emitted by red, green and blue LED chips, and due to such advantages, the LED has been commonly used as a light emitting element for various light emitting devices.
In particular, recently, an LED using a nitride-based semiconductor has been utilized as a white light source in a variety of fields for applications in devices such as a keypad, a backlight, a traffic light, an airstrip landing light, and a general illumination source.
An LED is a point source of light having the characteristics of straightness, and in order to utilize an LED as a light source for illuminating a large area, a plurality of LEDs are required to be regularly arranged in consideration of an illumination area and used.
Thus, in order to implement such a structure, LEDs are manufactured in a package form and then the LED packages are arranged in a row on a substrate such as a PCB so as to be manufactured, and in this case, a manufacturing unit cost is increased due to the manufacturing of the packages.
Thus, a chip-on-module (COM) scheme capable of obtaining advantages in terms of cost in comparison with the method for manufacturing respective LED packages is preferred.
According to the COM scheme, a plurality of LED chips are mounted on a module and manufactured, so there is no need to manufacture an LED package.
In addition, a light-transmissive cover, such as a lens, may be used in order to reduce the difference in a color temperature generated in a process using an LED chip and a phosphor for converting the wavelength of light so as to convert the color of light into a white light source and enhance light distribution by increasing the speed of light.
In a related art lens formation method, a plurality of LED chips are bonded on a substrate, phosphors are applied to the respective LED chips, and a lens is then individually implemented on each of the LED chips. Here, the manufacturing process is complicated and unit manufacturing cost is increased.
In this method, the lens is formed through a process such as dispensing by adjusting the viscosity and amount of a liquid material used for forming the lens.
However, a lens formed according to such a method is limited in the configuration. Namely, the form or shape of the lens is mostly fixed, making it difficult to change the shape of the lens into various forms in consideration of the characteristics of a light emitting device.
Also, individually formed lenses have a certain tolerance in the aspect of standardization, resulting in a severe dispersion in dimensions of respective products, which results in the dispersion of light emitted from the LED chips not being uniform.
In addition, if phosphors are applied to respective LED chips and individual lenses are used for that purpose, deviation of the color temperature generated between the LED chips and the phosphors is increased.
Meanwhile, light from an LED has optical characteristics of straightness, such that the lens for the LED is manufactured in the shape of a convex lens aimed at generally diffusing light to the lateral side, so as to be used.
However, when lenses are individually formed on the respective LED chips in configuring a light emitting device by arranging the plurality of LED chips on a substrate, an area in which light beams emitted from the respective LED chips are not mixed is generated.
This is called a spot phenomenon. In detail, when a light diffusion cover such as a lens is installed at the light emission side of an LED chip, a portion of the area of the light emitted from the LED chip appears to be brighter while another portion of the area appears to be darker.
Namely, when the transmittance of the lens is too high, the luminance of the area in which the LED chip is positioned is relatively high, so the area is seen to be brighter, while an area in which the LED chip is not installed is seen to be darker so as to be viewed as if there was a dot present.
In order to prevent such a spot phenomenon, the transmittance of the lens is required to be lowered by a certain numerical value, and in this case, if a lens having a low transmittance is used to prevent the occurrence of a spot phenomenon, the intensity of illumination by the respective LED chips becomes relatively weak, thereby degrading the illumination effect overall.
In order to resolve this problem, a larger number of LED chips are required to be installed densely on the substrate, causing the unit manufacturing cost to be increased.
Meanwhile, a conventional lens is made of a resin such as silicon in order to match a light refractive index, and in this case, silicon is relatively costly, so a method for reducing the usage of silicon is required.